PHILADELPHIA — An anonymous social media site has been identifying witnesses in violent crimes across Philadelphia with the stated intention of trying to “expose rats,” and city police were trying to find out who is behind it.

The “rats215” account on the San Francisco-based photo-sharing site Instagram has posted pictures, police statements and testimony identifying more than 30 witnesses since February, The Philadelphia Inquirer reported.

Police Lt. John Walker said investigators learned of the account last week when an officer monitoring Twitter spotted photos of a witness and court records from an attempted shooting last year. That led to the Instagram account, where officials found witness statements from the alleged 19-year-old victim, who said he was fired upon that summer because he had testified in a homicide case.

It remains unclear how rats215 obtained his testimony, the Inquirer reported. The case was handled by a secret indicting grand jury — a practice the Pennsylvania Supreme Court authorized last year to protect witnesses in violent crime prosecutions. The site also had names of witnesses, even though the names of witnesses and victims are redacted in court records for their protection.

The account, which was inaccessible by 8 p.m. Thursday, had nearly 7,900 followers and had been updated almost daily, The Inquirer reported. It had contained more than 150 photos, many drawing dozens of comments and likes.

“Post some new rats,” one commenter wrote in September, according to the Inquirer. “I needa put a hit out on them.”

One post praised drug dealer Kaboni Savage, who was sentenced to death for being behind a dozen murders including a firebombing that killed four children and two women. The bombing was retaliation for an informant’s cooperation with authorities and was among the worst witness revenge killings in city history.

Instagram would not say whether it took down the account, citing a policy of not publicly discussing individual accounts. But a spokeswoman said Friday that community guidelines do not allow content that bullies or harasses, and she said Instagram encourages people to report such content using a built-in tool next to every photo or video posted on Instagram.

Tasha Jamerson, a spokeswoman for the district attorney’s office, said she couldn’t comment on an investigation but called witness intimidation a “very serious, ongoing problem” that plagues Philadelphia prosecutors daily.

“We work with Philadelphia police to investigate vigorously and thoroughly any attempt to intimidate any witness, to identify perpetrators, and, where appropriate, arrest and prosecute,” she said in an email.

Veteran law enforcement officials say they have seen victims’ statements posted in barbershops, on neighborhood utility poles and even mailed to the homes of witnesses, but such statements now are as likely to wind up on Facebook, Twitter and Instagram.

Walker said investigators are now working to identify the accountholder.

“These actions shoot an arrow through the heart of the criminal justice system, placing victims and witnesses at risk,” he said.